Generally, polycarbonate resins have transparency, high impact strength, heat resistance and electrical properties. Therefore, polycarbonate resins have been widely used in the production of large injection molded products, such as electric or electronic goods and office equipment which emit a lot of heat. Accordingly, flame retardancy, heat resistance and high mechanical strength are important factors that should be considered when manufacturing a polycarbonate composition.
Conventionally to provide a polycarbonate resin with good flame retardancy, a halogen-containing flame retardant or an antimony-containing compound were used. However, halogen-containing compounds can corrode a mold due to hydrogen halide gases released during the molding process. In addition, there are safety concerns associated with the use of halogen-containing compounds because toxic gases can be liberated in the case of fire.
One method to impart flame retardancy to a polycarbonate resin without using a halogen-containing compound is to employ a phosphoric acid ester compound as a flame retardant. However, a juicing phenomenon can occur when using a phosphoric acid ester compound due to the migration of the flame retardant agent to the surface of the molded article during the molding process. Further, the heat resistance can be rapidly deteriorated.
EP 0 728 811 discloses a thermoplastic resin composition comprising an aromatic polycarbonate, a graft copolymer, a vinyl copolymer and a phosphazene. EP '811 states that no dripping occurs during combustion when using a phosphazene as a flame retardant even though an additional anti-dripping agent is not employed, and that the resin composition has excellent heat resistance and impact strength. However, in EP '811, when using phosphazene as a flame retardant, an increased amount of flame retardants should be used to maintain a certain degree of flame retardancy.